Up until the 1980s, there was dramatic growth in the creation of new surgical methods for treating a wide variety of previously untreated conditions. Over the past twenty years there has been a clear trend towards the invention of devices and methods that enable less-invasive treatment of such diseases, moving from invasive surgery, and then to less-invasive surgery, and to interventional techniques. Ultimately, it is desirable to move to totally non-invasive therapies.
The history of treatment of atrial fibrillation has followed this progression. First, Dr. James Cox invented a new open-heart surgical procedure that interrupted depolarization waves using surgical incisions in the walls of the atrium. More recently, a number of devices have been developed to allow surgeons to make such lesions during surgery on the beating heart, and without making incisions in the walls of the atrium. More recently, interventional electrophysiologists have worked with companies to develop catheter-based systems to create similar lesions. Although only partial success has been achieved to date, there is optimism for further progress within the next few years.
Still more recently, concepts have been proposed for completely non-invasive treatment of atrial fibrillation by using focused external high-energy gamma or electron beam radiation to create lesions in specific areas of the atria of the heart. While offering great promise, these technologies also may present significant issues, including the type of lesion created in the atrial wall by radiation, difficulty in creating specific lesions and focusing on moving tissue, and the potential for damage to surrounding tissues. Such methods also require a preliminary computed tomography (CT) scan to program the computer that guides the energy beam.
A wide variety of energy modes have been used to create lesions using epicardial or intracardiac probes. Radio-frequency electrical energy, microwaves, cryothermia probes, alcohol injection, laser light, and ultrasound energy are just a few of the technologies that have been pursued.
Separately, several groups have developed focused ultrasound devices with both imaging and therapeutic capabilities. These efforts began perhaps with lithotripsy, in which a high power focused ultrasound system developed by Dornier Medizintechnik, Germany, is used to break up kidney stones in the body. The kidney stones generally are located within the body at a significant depth from the skin. One ultrasound imaging system is used to aim the system at the kidney stones, and then a second, high energy ultrasound system delivers energy that breaks up the stones so they can be passed.
More recently, Therus Corp of Seattle, Wash., has developed a system to seal blood vessels after the vessels have been punctured to insert sheaths and catheters. The Therus system shrinks and seals femoral artery punctures at a depth of approximately 5 cm.
In addition, Timi-3 Systems, Inc., Santa Clara, Calif., has developed and is testing a trans-thoracic ultrasound energy delivery system to accelerate the thrombolysis process for patients suffering an acute myocardial infarction. This system delivers energy at a frequency intended to accelerate thrombolysis without damaging the myocardium or vasculature of the heart.
Epicor Medical, Inc. of Sunnyvale, Calif., has developed a localized high intensity focused ultrasound (“HIFU”) device to create lesions in the atrial walls. The Epicor device is a hand-held intraoperative surgical device, and is configured to be held directly against the epicardium or outside wall of the heart. When energized, the device creates full-thickness lesions through the atrial wall of the heart, and has demonstrated that ultrasound energy may be safely and effectively used to create atrial lesions, despite presence of blood flow past the interior wall of the atrium.
In addition, Transurgical, Inc., Setauket, N.Y. has been actively developing HIFU devices. However, while the Epicor Medical devices are placed in close approximation against the outside of the heart, the Transurgical devices are directed to intravascular catheters for heating or ablating tissue in the heart and require that the catheter be brought into close approximation with the targeted tissue.
In view of the aforementioned limitations of previously-known devices and methods, it would be desirable to provide methods and apparatus for treating atrial fibrillation or other conduction defects or ablating tissue at a distance from that tissue, so that the procedure may be performed non-invasively.
It also would be desirable to provide methods and apparatus for treating atrial fibrillation by applying energy from outside the body or from organs, such as the esophagus, that are easily accessible via natural body openings.